1. Field of the Invention
The present invention relates to a nitride-based semiconductor light emitting element and a light emitting device in which the nitride-based light emitting element is mounted in the package.
2. Description of Related Art
Because highly efficient blue-violet emission can be obtained from group III nitride semiconductors represented by gallium nitride, the semiconductors have attracted attentions as materials for Light Emitting Diodes (LEDs) and Laser Diodes (LDs). Among them, the LD with a wavelength of 405 nm is expected as a light source for an optical disk apparatus with a large capacity, because the beam of the LD can be more narrowed than the conventional LD with a wavelength of 650 nm. In recent years, with the spread of big-screen TVs, etc., there is an increasing demand for blue-violet reproducing LDs in order to reproduce high-quality moving images.
The structure of a typical nitride-based semiconductor light emitting element (semiconductor laser) is illustrated in FIG. 7. The nitride-based semiconductor light emitting element has a lamination structure in which an n-type cladding layer 102, an optical guide layer 103, an active layer 104, an optical guide layer 105, and a p-type cladding layer 106 are laminated on a GaN substrate 101 in this order. The p-type cladding layer 106 is processed into a ridge shape. The top of the ridge is covered with an insulating film 107 having a stripe-shaped aperture in which a p-type electrode 108 is provided. A current blocking structure is formed by a stripe-shaped electrode and the transverse mode is controlled by adjusting the width and height of the ridge. A laser beam is radiated from a resonator mirror (not illustrated) formed by cleavage.
A dielectric film (not illustrated) is formed, as an end-surface protective film, on the resonator mirror formed by cleavage. As end-surface protective films for the blue-violet semiconductor laser with a wavelength of 405 nm, for example, an Anti-reflecting (AR) film composed of an Al2O3 single layer is provided on the surface on the side where a laser beam is radiated, and a High-reflecting (HR) film composed of a multilayer film such as Al2O3/TiO2, is provided on the surface opposite to the forgoing surface. With such a configuration, the surface of the semiconductor is protected and the oscillation threshold current is reduced, thereby allowing a lease beam to be efficiently radiated from the surface on which the AR film is provided.
The semiconductor light emitting element thus manufactured is enclosed in a CAN package to be easily incorporated into an optical pickup device. Specifically, after the semiconductor light emitting element has been fusion-bonded to a heatsink followed by fusion bonding thereof to a stem, the stem is enclosed with a cap having a glass window. With such a package, it can be prevented that the semiconductor light emitting element may be damaged during assembly work, and it becomes possible that the heat radiation property during a light emitting operation is secured to stably operate the semiconductor light emitting element.
Herein, the oscillation wavelength of a blue-violet semiconductor light emitting element is as short as 405 nm and the photon energy of the laser beam is as high as 3.0 eV. Therefore, there arises the problem that organic matters remaining in the atmosphere are chemically degraded by the light emitted by the semiconductor light emitting element, and accordingly impurities such as carbon, silicon, or the like, adhere to the surface of the semiconductor light emitting element on the side where light is radiated.
Accordingly, Japanese Unexamined Patent Publication No. 2004-289010 describes a light emitting device in which adhesion of impurities to a semiconductor light emitting element can be suppressed by restricting the vapor pressure of the silicon organic compound gases in a CAN package.
Also, Japanese Unexamined Patent Publication No. 2006-344727 describes a method of manufacturing a laser device in which adhesion of impurities to a semiconductor light emitting element during a light emitting operation is suppressed with the organic gases in the CAN package being degraded and annihilated by radiating the light with a wavelength of 420 nm or less into the CAN package, while the CAN package into which the semiconductor light emitting element has been enclosed is being heated to 70° C. or higher.
Also, Japanese Unexamined Patent Publication No. 2004-40051 describes a technique in which a semiconductor light emitting element is enclosed in the CAN package after organic matters have been eliminated by radiating ultraviolet light or plasma onto a semiconductor light emitting element support member. Also, Japanese Unexamined Patent Publication No. 2004-273908 describes a technique in which ultraviolet light is radiated into the CAN package after a semiconductor light emitting element has been enclosed in the CAN package under an ozone atmosphere.
Also, Japanese Unexamined Patent Publication No. 2008-182208 describes a technique regarding a nitride-based semiconductor light emitting element.